(a) Field of the Invention
The present invention relates an organic electroluminescent (hereinafter referred to as xe2x80x9cELxe2x80x9d) device having an excellent long-term moisture resistance, and a method for fabricating the same.
(b) Description of the Related Art
In a field of a flat display device, an organic EL device including an organic luminescent layer between an anode and a cathode has been conventionally proposed, and researches therefor are actively conducted. However, such an organic EL device is affected by surrounding moisture and has a poor moisture resistance. Ingress of water contents to the interface between the organic luminescent layer and the electrode prevents injection of electrons, thereby generating dark spots showing a non-luminescent region, or corroding the electrodes.
JP-A-10(1998)-312883 describes an organic EL device covered with a buffer layer made of thermoplastic resin and a barrier layer made of an inorganic material. However, in the organic EL device described therein, the ingress of the moisture from the interfaces between the organic EL device and the above layers cannot be sufficiently eliminated. In addition, the EL device has larger dimensions due to these layers. Further, the stress caused by the formation of these layers reduces the luminescent efficiency of the organic EL device or destroys the organic EL device depending on circumstances.
JP-A-10(1998)-275679 describes an organic EL device sealed with sealing glass having a moisture-absorbing porous layer such as a SiO2 layer, a TiO2 layer and a zeolite layer. Since, however, the moisture absorption by the porous layer utilizes only physical adsorption, the influence of the moisture cannot be sufficiently eliminated. In addition, since the surface area of the porous layer is reduced by the inner wall area of the sealing glass, the elimination of the moisture influence for a longer period of time is difficult.
JP-A-9(1997)-148066 describes an organic EL device in which a desiccant maintaining a solid state even after absorbing moisture is fixed in a sealing can by using an adhesive.
Since, however, the amount of the desiccant which can be fixed by the adhesive is restricted by the surface area of the inner wall of the sealing can, the smaller amount of the desiccant cannot effectively eliminate moisture influence for a longer period of time. In addition, since the employable desiccants are limited to one that maintains the solid state even after absorbing moisture, use of a hygroscopic desiccant or a deliquescent desiccant is difficult.
In view of the foregoing, an object of the present invention is to provide an organic EL device having an excellent long-term moisture resistance and generating less number of dark spots, by using various desiccants in a sufficient amount.
It is another object of the present invention to provide a method for efficiently fabricating such an organic EL device having the excellent long-term moisture resistance.
The present invention provides, in a first aspect thereof, an organic EL device including: a transparent substrate; a stacked structure formed on the transparent substrate, the stacked structure including an anode, a cathode and at least one EL layer sandwiched between the anode and the cathode; a sealing can for encapsulating the stacked structure together with the transparent substrate; and a desiccant-containing layer formed on an inner surface of the sealing can.
The present invention provides, in a second aspect thereof, a method for fabricating en organic EL device including the steps of: forming a stacked structure on a transparent substrate, said stacked structure including an anode, a cathode and at least one organic EL layer sandwiched between the anode and the cathode; forming a desiccant-containing layer on an inner surface of a sealing can; and encapsulating the stacked structure using at least the sealing can.
In accordance with the first and the second aspects of the present invention, since a considerable amount of a desiccant, especially a variety of desiccants, can be contained in the desiccant-containing layer on the sealing can to exclude moisture infiltrated from the interface between the transparent substrate and the sealing can, the organic EL device having an excellent long-term moisture resistance, and especially generating no or a few dark spots, can be provided. In a preferred embodiment thereof, a concave-convex surface formed on the sealing can prevents the release of the desiccant-containing layer from the sealing can to secure the long-term moisture resistance.
Such an organic EL device having the excellent long-term moisture resistance can be fabricated by the method of the present invention. In a preferred embodiment of the method, the desiccant-containing layer forming step and the stacked structure sealing step can be simultaneously conducted to reduce the number of the steps for the fabrication.
The above and other objects, features and advantages of the present invention will be more apparent from the following description.